Among various foam discharge pump dispensers, there is already a foam dispensing pump container which has the U.S. Pat. No. 5,443,569. The above foam discharge container has (1) a structure that liquid of an air and liquid mixing chamber can flow into an air chamber in a reverse direction, and (2) an air valve for controlling an input and output of air is made of a very thin plastic ejection resin, so that it transforms when a certain impact is applied or a pressure is applied as an external force is applied in the course of an assembling work. (3) Noise (plosive sound) occurs as the air valve comes in contact with the air in the course of pumping. (4) Since a return spring is provided in the liquid cylinder, it is in contact with liquid, so that liquid may change due to corrosion of the metallic spring.
The problems encountered in the above conventional art will be described in more detail. Liquid sucked into the interior of a liquid piston is inputted into an air and liquid mixing chamber. When it is discharged in a mixed state with air, a reverse flow into an air chamber by means of the pressure of air inputted from the air chamber is prevented. However, when a nozzle head moves up or stops, a small amount of liquid filled in the interior of the air and liquid mixing chamber often flow in a reverse direction into the air chamber via along an air inlet passage. As the above reverse flow phenomenon frequently occurs, a relatively lot of liquid is gathered in the air chamber, so that the volume of the air chamber reduces. The air charging amount may decreases due to the reduced volume in the air chamber, so that a mixing ratio of air and liquid supplied into the air and liquid mixing chamber becomes unreliable. Therefore, it is impossible to obtain uniform foams. In worse case, the liquid may be directly discharged without foam. When the liquid exists in the air chamber for a long period of time, the sealing function of the air piston decreases due to a solidification phenomenon to occur within the chamber. In further worse case, the air piston may not properly work.